Method for manufacturing a semiconductor device

ABSTRACT

A method for forming a silicon island used for forming a TFT or thin film diode comprises the step of pattering a silicon film with a photoresist mask. In order to prevent the contamination of the semiconductor film due to the photoresist material, a protective film such as silicon oxide is interposed between the semiconductor film and the photoresist film. Also, the protective film is preferably formed by thermal annealing or light annealing in an oxidizing atmosphere.

This application is a Continuation of Ser. No. 08/275,638 filed Jul. 15,1994, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing asemiconductor device which includes a non-single crystallinesemiconductor layer formed on a substrate, for example, an insulatingsubstrate such as glass. In particular, the semiconductor device is ofan insulated gate type such as a thin film transistor (TFT) or thin filmdiode (TFD). The present invention is further related to a manufactureof a thin film integrated circuit utilizing the TFT or TFD, specificallya thin film integrated circuit for an active matrix liquid crystaldisplay device.

DESCRIPTION OF PRIOR ART

In recent years, active matrix liquid crystal device and an image sensorhave been developed which utilize a semiconductor device having TFTsformed on an insulating substrate such as glass for driving pixels or asa peripheral circuit.

Silicon in the form of a thin film is most generally used for formingTFTs of these semiconductor devices. Generally, thin film siliconsemiconductors are classified to (a) amorphous silicon and (b)crystalline silicon. While amorphous silicon is easy to form at arelatively low temperature, electrical characteristics of the amorphoussilicon is inferior to crystalline silicon.

In usual, when manufacturing TFTs with a silicon film, a pattering ofthe silicon film has been used to isolate each element from one another.A photoresist has been used to pattern the silicon film as a mask.

On the other hand, it has been strongly required to avoid anycontamination of silicon during the fabrication process of TFTs as muchas possible since an active semiconductor region of a TFT is verysensitive to impurities. As a source of a contamination, the air and thehandling with human hands are known. However, this problem has not beencompletely solved yet.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductordevice such as a TFT or image sensor having a high quality by solvingthe foregoing problems.

It is another object of the present invention to provide a semiconductordevice having a semiconductor film with an improved crystallinity.

The inventors of the present invention first recognized that aphotoresist which is used for patterning a semiconductor layer is one ofthe sources of the contamination causing properties of the TFTs degrade.Based on this recognition, the primary feature of the invention is toprovide a protective film between the photoresist and the semiconductorlayer in order to prevent the impurity elements contained in thephotoresist from invading into the semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing feature and other features of the invention will bedescribed in detail with reference to the attached drawings in which:

FIGS. 1A-1E show cross sectional diagrams showing a manufacturingprocess in accordance with a first example of the invention;

FIGS. 2A-2E show cross sectional diagrams showing a comparative exampleof the present invention;

FIGS. 3A-3E show cross sectional diagrams showing a manufacturingprocess of the second example of the invention;

FIGS. 4A-4E show cross sectional diagrams showing a manufacturingprocess of the third example of the invention;

FIGS. 5A-5E show cross sectional diagrams showing a manufacturingprocess of the fourth example of the invention;

FIGS. 6A-6C show a TFT manufactured in accordance with the fifth exampleof the invention; and

FIG. 7 shows a relation among thickness, oxidation period and oxidationtemperature with respect to a thermal oxide film in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF INVENTION

In this invention, inorganic materials such as silicon oxide or siliconnitride or a mixture thereof are usable as a blocking layer which is tobe formed on a semiconductor layer prior to a provision of a photoresistthereon. In particular, the blocking layer comprises an oxide which isformed by oxidizing a surface of the semiconductor layer. Namely, theoxide is formed by subjecting the semiconductor to a heat annealing at asuch a temperature that the substrate is not damaged or to aphotoannealing, in an oxidizing atmosphere such as oxygen, oxygennitride and ozone. Also, in this invention, the photoannealing means aprocess in which a laser light or a light having an enough intensity asequivalent to laser light is used. Usable as light sources areindustrially available lasers such as excimer laser, YAG laser, CO₂laser or ruby laser, xenon lamp, krypton arc lamp, halogen lamp and thelike.

When employing the heat annealing in this invention, it is desirable touse a temperature which does not cause a substrate bend or contract, forexample, it is preferable to use a temperature ranging 400° C. to 700°C., more preferably 500° C. to 600° C. The thickness of the oxide can becontrolled by changing the temperature and the length of the heatannealing. In this invention, it is desirable to make the oxide layerpinhole free and as thin as possible, for example, 20Å to 100Å.

Also, it is possible to use a higher temperature if there is nopatterning provided on the substrate. Furthermore, if the substrate isprovided with a pattern, although it is desirable to use a temperaturewhich is lower than a strain point of the substrate, a highertemperature may be used if the substrate is thermally treated in advancein order to release internal stress of the substrate and thus tominimize a contraction of the substrate in the subsequent heating step.

The foregoing explanation is also applicable to a photoannealing.However, the use of a pulsed laser is advantageous in that the substrateis not heated in either partly or wholly. Also, it is more effective toheat a substrate at not higher than 600° C., preferably not higher than400° C. during the photoannealing. Further, both of the photoannealingand heat annealing may be employed in turn or simultaneously. Forexample, the photoannealing may be done after the heat annealing or viceversa.

The semiconductor layer may have either one of an amorphous structure orcrystalline structure when performing the foregoing treatments. In thecase of crystallizing a silicon film by heating, it is possible tocrystallize it at a lower temperature than usual solid phasecrystallization temperature by using a metal element such as nickel forpromoting the crystallization. As the metal element for promoting thecrystallization usable are VIII group elements of Fe, Co, Ni, Ru, Rh,Pd, Os, Ir, and Pt and other elements such as Sc, Ti, V, Cr, Mn, Cu, Zn,Au and Ag. Moreover, it is possible to further increase thecrystallinity of the silicon film after this low temperature heating, bysubjecting it to a laser annealing or a light annealing with asufficiently intense light.

FIG. 7 shows a relation among thickness of a thermal oxide film,duration of oxidation process and heating temperature with respect to anoxide film formed by the low temperature heat oxidation. A singlecrystalline silicon wafer and a crystalline silicon film which isobtained by growing an amorphous silicon film in a solid phase are usedto be subjected to the oxidation. Also, the thickness of oxide films isobtained in a manner in which a thermal oxide film is obtained byheating a single crystalline silicon wafer at 900° C., the thickness ofthis oxide film is measured by an elipsometry method, then the thicknessof the target film is calculated from an etching period thereof by usingan etching rate of the 900° C. thermal oxide film. It is to beunderstood from FIG. 7 that the crystalline silicon film is oxidized twotimes faster than the single crystalline silicon wafer. Also, there isno tendency observed that the thickness of the oxide film of thecrystalline silicon film saturates with respect to the oxidationduration.

In accordance with the present invention, a thermal oxide film having30Å to 60Å thickness can be obtained for about 30 minutes by annealingat 550° C. in a dry oxygen. This oxide film is pinhole free, dense anduniform in thickness. Also, the interface between the silicon layer andthe oxide layer is very excellent. It should be noted that the interfacecondition is not so excellent in the case of forming the oxide layer bysputtering because the surface of the silicon is damaged.

Because of the excellent interface condition, an excellent siliconsurface can be obtained after removing the oxide film. Therefore, if thesemiconductor film is used for a TFT, various characteristics (carriermobility, subthreshold value (S-value) or the like) and the reliabilitycan be improved.

In the case of using a photoannealing, the thickness of the oxide filmis determined by the total amount of the light incident on the surface.The interface condition in the case of the photoannealing is asexcellent as that in the case of the heat annealing. Thus, an excellentTFT can be obtained.

EXAMPLE 1

FIGS. 1A through 1E show cross sectional views of a manufacturingprocess in accordance with the first example of the present invention.

Initially, a silicon oxide film 12 is formed on a substrate 11 (Corning7059) by sputtering to a thickness of 2000Å. It is preferable to heatthe substrate prior to or after the formation of the silicon oxide film12 at a temperature higher than a strain point of the substrate and thencool it below the strain point at a cooling rate of 0.1-1.0° C./minute.This treatment suppresses the contraction of the substrate due tosubsequent heating steps (including the oxidation process of theinvention with IR radiation or heat annealing), making a mask aligningprocess easier. In the case of the Corning 7059 like in this example,the substrate is heated at a temperature 620°-660° C. for 1 to 4 hoursthen cooled to 450-590° C. at cooling rate of 0.1-1.0° C., preferably0.1-0.3° C., at which temperature the substrate is taken out.

Then, an amorphous silicon film 13 is deposited on the silicon oxidefilm 12 by a plasma CVD to a thickness of 500Å to 1500Å, for example,1000Å. Further, a silicon oxide film 14 is formed on the amorphoussilicon 13 by a plasma CVD to a thickness of 1000Å. The silicon oxidefilm 14 functions as a protective film ("cap-layer") when subjecting theamorphous silicon to thermal crystallization. For forming the siliconoxide film 14, tetraethoxysilane Si(OC₂ H₅)₄ (so called TEOS) and oxygenare used as a precursor gas in the plasma CVD. The substrate temperatureduring the deposition is 200-450° C., for example, 250° C. Then, theamorphous silicon film 13 is crystallized by heating at 600° C. for 48hours in nitrogen at the atmospheric pressure. The thickness of thecap-layer should be at least 500Å in order to improve the density andthe surface condition of the crystalline silicon film.

After the crystallization, the silicon oxide film 14 is removed byetching using a water solution of 1/10 HF and fluoride ammonium(1/10BHF) as an etchant. Thus, the surface of the silicon film 13 isexposed as shown in FIG. 1B.

Then, in accordance with the present invention, the surface of thesilicon film 13 is thermally oxidized in a flow of oxygen (7 cm³/second) at 550° C. to 600° C. As a result, a silicon oxide film 15 isobtained to a thickness of 40-50Å as shown in FIG. 1C.

Subsequently, the silicon film 13 is patterned by a knownphotolithography with a photoresist mask (not shown in the figure) tothus obtain a silicon island 17 as shown in FIG. 1D. The thermal oxidefilm 15 functions as an impurity blocking layer from the photoresist.The reason of using the 1/100 HF solution rather than the strongeretchant like 1/10 BHF used in the previous step is that thecontrollability of the etching process can be improved by increasing theetching period of the silicon oxide film and thus minimizing theoveretching of the underlying silicon film. As a result, the value "y"of the overetching in this example can be suppressed as small as 80Å-90Å. (FIG. 1E)

Finally, the silicon oxide film 15 is etched using a 1/100 HF solution.Accordingly, a silicon island can be formed while a contamination by thephotoresist is prevented.

EXAMPLE 2

The process in the second example of this invention will be described inconjunction with FIGS. 3A-3E. A Corning 7059 glass substrate (1.1 mmthick, 300 mm×400 mm) is used as a substrate 31. In the same manner asin the first example, the substrate is initially heated at 640° C. forone hour and then cooled to 580° C. at a cooling rate of 0.2° C./minute.A silicon oxide is deposited on the substrate 31 as a blocking layer 32to a thickness of 2000Å by a plasma CVD. TEOS is used as a precursor gasand the substrate is maintained at 350° C.

Then, an amorphus silicon layer 33 is formed to a thickness of 500Å by aLPCVD or plasma CVD on the blocking layer 32. Further, a silicon oxidelayer 34 having a thickness of 1000Å is provided on the amorphoussilicon layer 33 through a plasma CVD, following which a portion of theamorphous silicon 33 is exposed by patterning the silicon oxide layer bya known photolithography. Then, a thin nickel film 35 (10Å or less) isformed on the amorphous silicon layer 33 as shown in FIG. 3A.

Subsequently, the substrate is heated at 550° C. for 8 hours, or at 600°C. for 4 hours in nitrogen atmosphere in order to proceed acrystallization of the silicon film 33 in a direction shown by arrows ofFIG. 3B by virtue of the crystallization promoting effect of the nickel.

After the crystallization, the silicon oxide layer 34 is removed with a1/10BHF solution used as an etchant so that the surface of the siliconlayer 33 which has been crystallized is exposed. (FIG. 3C)

Then, in accordance with the present invention, the silicon layer 33 issubjected to an oxygen flow (7 cm³ /second) at 550° C. for one hour inorder to form a silicon oxide layer 37 on the surface of the siliconlayer as shown in FIG. 3D.

Next, the silicon layer 33 together with the silicon oxide layer 37 ispatterned into a silicon island 38 by a known photolithography. At thistime, care should be taken to remove the portion of the silicon film onwhich the nickel film was directly formed (see FIG. 3A) and to removethe portion which corresponds to a top end of the crystallization shownby the arrow of FIG. 3B. Subsequently, the silicon oxide layer 37 whichremains on the silicon island 38 is removed by etching with 1/100HFsolution as an etchant.

EXAMPLE 3

The process of the third example of this invention will be described inconjunction with FIGS. 4A to 4E. The same substrate 41 having a siliconoxide layer 42 and an amorphous silicon layer 43 is prepared in the samemanner as in the previous examples.

On the amorphous silicon film 43, a photoresist layer 44 is provided byspin coating to a thickness of 2 gm, following which the photoresistlayer is patterned by a known photolithography in order to expose aportion of the silicon layer. Further, a nickel film 45 of a thickness10Å or less is formed by a sputtering method. (FIG. 4A)

Then, as shown in FIG. 4B, the photoresist layer 44 is removed by aknown process while the nickel film directly formed on the portion ofthe silicon layer (as designated with a reference numeral 46) remainsunremoved.

Then, the substrate is heated at 550° C. for 8 hours, or at 600° C. for4 hours in a nitrogen gas. As a result, the silicon layer iscrystallized in a direction shown by the arrows in FIG. 4C by virtue ofthe crystallization promoting effect of the nickel.

Subsequently, the substrate is dipped in a nitric acid solution in orderto form an oxide layer on the silicon layer. Then, this oxide film isremoved by using 1/10BHF as an etchant. These steps are repeated severaltimes. As a result, the surface of the silicon film is sufficientlycleaned and finally can expose a clean surface of the silicon layer eventhough the silicon film is once contacted with the photoresist layer.

Then, referring to FIG. 4D, a silicon oxide 47 is formed on the siliconlayer by thermally oxidizing the surface with a plasma of oxygenactivated by microwave, at 200-400° C., for example, 300° C. Thethickness of the silicon oxide layer is 40 to 60Å.

Finally, the silicon layer together with the silicon oxide layer ispatterned through a known photolithography to form a silicon island 48in a manner in that the region to become an active region of a TFT orTFD does not contain the added nickel at a high concentration.Thereafter, the silicon oxide layer 47 which remains on the siliconisland 48 is etched off with a 1/100HF solution.

EXAMPLE 4

The process in accordance with the fourth example of the invention willbe described in conjunction with FIGS. 5A-5E. Further, a description formanufacturing a TFT will be made.

Initially, the substrate 51 having the silicon oxide layer 52 and theamorphous silicon layer 53 is prepared entirely in the same manner as inthe previous examples so that redundant explanations are omitted here.

On the amorphous silicon layer 53 formed on the substrate 51, a siliconoxide layer 54 is deposited to a thickness of 1000Å through a plasmaCVD, following which the silicon oxide layer is patterned to expose aportion of the silicon layer 53. A nickel film 55 of 200 Å thick isformed thereon by sputtering as shown in FIG. 5A.

Then, the substrate is heated at 450° C. for one hour. As a result, anickel silicide layer 56 in the region where the nickel is directlyformed on the silicon layer as shown in FIG. 5B. Thereafter, the siliconoxide layer 54 is removed with 1/10BHF to expose the surface of thesilicon layer 53.

Then, a silicon oxide layer 57 is formed to a thickness of 40-60Å bythermally oxidizing the surface of the silicon film in an oxygen flow (7cm³ /second) at 550° C. for one hour as shown in FIG. 5C.

Subsequently, the oxygen gas is replaced by nitrogen in the furnace. Thesubstrate is heated in nitrogen at 550° C. for 8 hours, or at 600° C.for 4 hours in order to crystallize the silicon film 53 by virtue of thecrystallization promoting effect of the nickel. (FIG. 5D)

Then, a silicon island 59 is formed by pattering through a knownphotolithography process so that an active region of a semiconductordevice such as TFT is defined. Thereafter, the silicon oxide layer 57which remains on the silicon island is removed by using 1/100HF solutionas an etchant.

Using, the silicon island 59 thus obtained, a TFT is manufactured havinga structure shown in FIGS. 6A-6C. FIG. 6C shows a plan view of the TFT.FIGS. 6A and 6B show A--A' and B--B' cross sections of FIG. 6C,respectively. Reference numeral 63 designates source and drain regions,64 a channel region, 65 a gate insulating layer, 66 a gate electrode, 67an oxide layer, 68 an interlayer insulating layer, 69 source/drainelectrodes. In accordance with the present invention, since anundesirable overetching of the silicon oxide layer can be minimized, thegate insulating layer 65 and the gate electrode 66 can be formed with agood step coverage.

Further, as a material of the gate electrode, an aluminum alloy to whichscandium is added at 18% is used. The oxide layer 67 is formed byanodizing this gate electrode. During the anodic oxidation, since thereis little overetching at an edge of the silicon island, the gateelectrode can be prevented from being broken. Thus, the production yieldcan be improved.

The characteristics of the TFT thus obtained are as follows: a mobilityis 110-150 cm² /Vs and S value 0.2-0.5 V/digit in the case of NTFT, amobility 90-120 cm² /Vs and S value 0.4-0.6 V/digit in the case of PTFT.The mobility can be increased by more than 1.2 times as compared withthose of the conventionally obtained TFTs, and also the S value can bereduced to a half-value of the conventional value. The inventorsconsider this is because of the use of the thermal oxidation film whenpatterning the silicon film as a blocking film.

EXAMPLE 5

Referring again to FIGS. 3A-3E, the process of the fifth example of thisinvention will be described. Basically, the manufacturing process is thesame as that of the second example except that the irradiation of KrFexcimer laser (wavelength 248 nm) is used to form an oxide layer of thesilicon film instead of thermal annealing of the second example. In thesame manner as in the second example, a substrate is heated at 640° C.for an hour and then cooled at 0.2° C./min. to 580° C. in advance. Also,the underlying film 32 (silicon oxide, 2000Å thick), amorphous siliconlayer 33 (500Å thick) and the silicon oxide layer 34 (1000Å thick) areformed. A portion of the silicon layer is exposed by selectivelyremoving the silicon oxide film as shown in FIG. 3A.

Then, in this example, a thin nickel acetate film 35 is formed by spincoating. As a solvent, water or ethanol is used. Also, the concentrationof the nickel acetate is 10-100 ppm.

Then, the substrate is heated at 550° C. for 8 hours so that thecrystallization proceeds in a direction shown by arrows in FIG. 3B. Thenickel functions to promote the crystallization.

After the silicon oxide film 34 is removed with 1/10BHF used as anetchant to expose the surface of the silicon film 33 as shown in FIG.3C, the substrate is placed in an oxidizing atmosphere. Here, thesurface of the silicon film is irradiated with the KrF excimer laser.The energy density is 250-450 mJ/cm², for example, 300 mJ/cm². The laserirradiation is done at 10-50 shots per one place. As a result, thesilicon oxide layer 37 having a thickness of 10-50 Å is obtained. Theenergy density and the number of shots of the laser may be selecteddepending on the thickness of the silicon film 37 to be crystallized.Also, after the laser irradiation, a thermal annealing may be againperformed after the laser irradiation in the above mentioned condition.

After the crystallization, the silicon film is patterned to remove theportion thereof on which the nickel acetate film is directly formed andthe portion in which a top end of the crystals exist (corresponding tothe top of the arrows in FIG. 3B). After that the silicon oxide layer 37remaining on the silicon island is removed by using 1/100 HF solution.(FIG. 3E).

Instead of the laser, a halogen lamp may also be used. In this case, theirradiation duration should be controlled in order not deform thesubstrate due to the heat. With the thus formed silicon island, a TFTmay be formed. Of course, a plurality of silicon islands may be formedon one substrate using the process of the invention and an array of TFTsmay be formed.

COMPARATIVE EXAMPLE

Referring to FIGS. 2A-2E, a blocking layer 22 comprising silicon oxidewas initially formed on a substrate 21 and then an amorphous siliconlayer 23 was deposited by known method. Then, a protective layer 24 ofthe present invention such as silicon oxide, silicon nitride or the likewas formed by physical vapor deposition (e.g. sputtering) or a chemicalvapor deposition (e.g. plasma CVD, photo CVD).

Further, a photoresist pattern 25 was formed by a known photolithographyprocess. (FIG. 2A)

In this example, however, because the CVD or PVD were used, the obtainedfilms are relatively porous as compared with the oxide layer obtained inthe previous examples, therefore, it was necessary to use a thickerfilm, for example, several hundreds Å thick in order to ensure that thecontamination of the silicon film by the photoresist is safely avoided.

The silicon film 23 together with the protective film 24 was patternedby dry or wet etching to pattern the silicon film 23 into an island 26with the protective film 27 remaining thereon.

After removing the photoresist 25, the remaining protective film 27 wasremoved by wet etching as shown in FIG. 2C. At this time, because theprotective film 27 was relatively thick, the underlying silicon oxidefilm 22 was overetched. The value of the overetching "y" was 500Å. (FIG.2C) Therefore, a void 28 was unavoidably formed. The degree of theoveretching "y" is determined by the difference in etching rate and inthickness between the protective layer 24 and the underlying layer 22.In this case, since a same material was used for both layers, it isunavoidable that the underlying layer is etched at at least thethickness of the protective layer 24. Also, since it is necessary tocompletely remove the protective layer 27, the degree of the overetching"y" naturally increases.

Although there is a possibility to select a material of the underlyingfilm so that it has a higher etching resistivity than the protectivelayer 27, silicon oxide is most appropriate when considering thematching with the silicon semiconductor layer.

Consequently, because of the large degree of the overetching, a void 28tends to be formed causing a decrease in the step coverage of the gateinsulating layer 29 and the gate electrode 30 which are formed in thelater step. Accordingly, the insulation between the gate electrode andthe active layer can not be improved and a leak current tends to occur.

In particular, an etchant tends to penetrate through the void 28 so thatit is likely that the gate electrode is etched from the lower surfaceand broken. In the same manner, if the gate electrode is oxidized byanodic oxidation in an electrolyte, the oxidation proceeds not only onthe upper surface of the gate electrode but also on the portion close tothe void 28, causing a breaking of the wiring also.

Accordingly, it is desirable to utilize a protective film which issufficiently thin to minimize the overetching of the underlying film butis sufficiently dense and pinhole free. Therefore, the use of light orheat oxidation is preferable to achieve the purpose of the presentinvention. However, if a sufficiently dense and pinhole free film isobtainable even with a CVD, such a method should also be suitable to thepresent invention.

In accordance with the preferred embodiments of the invention, theoveretching of the underlying film during the formation of thesemiconductor islands can be reduced, a step coverage of the gateinsulating layer and the gate electrode is improved, and further a leakcurrent between a gate electrode and a silicon layer is reduced. Inparticular, because of the use of the protective film which is formed bythermal or light oxidation at 20-100Å, it is possible to suppress theoveretching to 100Å or less.

Also, in accordance with another aspect the invention, a gate insulatinglayer can be formed by forming a thin oxide layer (30-300Å) by thethermal oxidation or light oxidation, following which another siliconoxide film is laminated thereon by a conventional CVD. Thus, it ispossible to completely stop the void (gap) 70 shown in FIG. 6A.

While several examples have been descried, the present invention shouldnot be limited to these particular examples. Many modifications may bemade without departing the scope of the appended claims. For example,although only a photoresist has been disclosed as a mask material, theforegoing teaching should be applicable to any mask material.

What is claimed is:
 1. A method for manufacturing a semiconductor devicecomprising the following sequential steps of:forming a crystallizedsemiconductor film comprising silicon containing a catalyst metal forpromoting crystallization of said semiconductor film on an insulatingsurface of a substrate; treating a surface of said semiconductor film inan oxidizing atmosphere after forming said crystallized semiconductorfilm with a thermal annealing at 400-700° C. or with a photo annealingto form an oxide layer on said semiconductor film; coating a photoresiston said oxide layer; selectively etching said oxide layer and saidsemiconductor film; removing said photoresist to expose said oxide layerunder said photoresist; and removing said oxide layer.
 2. The method ofclaim 1 further comprising the step of irradiating said silicon filmwith a light.
 3. A method for manufacturing a semiconductor devicecomprising the following sequential steps of:forming an amorphoussemiconductor film comprising silicon on an insulating surface of asubstrate; forming a layer in contact with said amorphous semiconductorfilm which contains a catalyst metal for promoting crystallization ofsaid semiconductor film; crystallizing said amorphous semiconductorfilm; exposing a surface of said semiconductor film to an oxidizingatmosphere after said crystallizing; treating said surface in saidoxidizing atmosphere with a thermal annealing at 400-700° C. orphotoannealing in order to form an oxide layer on said semiconductorfilm; forming a photoresist on said oxide layer; selectively etchingsaid oxide layer and said semiconductor film; and removing saidphotoresist and said the oxide layer under said photoresist.
 4. Themethod of claim 3 further comprising the step of heating said amorphoussilicon film at 400-700° C. in order to crystallize said film.
 5. Themethod of claim 3 further comprising the step of crystallizing saidamorphous silicon film in a horizontal direction.
 6. A method formanufacturing a semiconductor device comprising the following sequentialsteps of:forming a silicon oxide layer over a substrate; forming anon-single crystalline semiconductor layer on said silicon oxide layer;disposing a catalyst capable of promoting crystallization of saidsemiconductor layer in contact with said semiconductor layer;crystallizing said semiconductor layer with the aid of said catalyst;exposing a surface of said semiconductor layer to an oxidizingatmosphere with heating after crystallizing said semiconductor layer inorder to oxidize the surface of said semiconductor layer to form anoxide layer thereon; selectively forming a mask on said semiconductorlayer with said oxide layer interposed therebetween, said maskcomprising an organic material; selectively etching said semiconductorlayer together with said oxide layer by using said mask; and removingsaid mask and said oxide layer underlying said mask.
 7. The method ofclaim 6 wherein said semiconductor layer comprises silicon.
 8. Themethod of claim 6 wherein further comprising source and drain regionswithin said semiconductor layer.
 9. The method of claim 6 wherein saidsemiconductor layer is heated at 400-700° C. in said oxidizingatmosphere.
 10. The method of claim 6 wherein said mask comprises aphotoresist.
 11. The method of claim 6 wherein said oxide layer isremoved by wet etching.
 12. A method for manufacturing a semiconductordevice comprising the steps of:forming a silicon oxide layer over asubstrate; forming a non-single crystalline semiconductor layer on saidsilicon oxide layer; disposing a catalyst metal containing material incontact with said non-single crystalline semiconductor layer;crystallizing said semiconductor layer with said catalyst metalcontaining material; exposing a surface of said semiconductor layer toan oxidizing atmosphere while irradiating said semiconductor layer withlight in order to oxidize the surface of said semiconductor layer toform an oxide layer thereon after crystallizing said semiconductorlayer; selectively forming a mask on said semiconductor layer with saidoxide layer interposed therebetween, said mask comprising an organicmaterial; selectively etching said semiconductor layer together withsaid oxide layer by using said mask; and removing said mask and saidoxide layer underlying said mask.
 13. The method of claim 12 whereinsaid semiconductor layer comprises silicon.
 14. The method of claim 12wherein further comprising source and drain regions within saidsemiconductor layer.
 15. The method of claim 12 wherein said maskcomprises a photoresist.
 16. The method of claim 12 wherein said oxidelayer is removed by wet etching.
 17. The method of claim 12 wherein saidlight is emitted from a light source selected from the group consistingof excimer laser, YAG laser, CO₂ laser, ruby laser, xenon lamp, kryptonarc lamp and halogen lamp.
 18. The method of claim 1 wherein saidcatalyst metal is at least one selected from the group consisting of Fe,Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Sc, Ti, V, Cr, Mn, Cu, Zn, Au and Ag.19. The method of claim 3 wherein said catalyst metal is at least oneselected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir,Pt, Sc, Ti, V, Cr, Mn, Cu, Zn, Au and Ag.
 20. The method of claim 6wherein said catalyst comprises at least a metal selected from the groupconsisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Sc, Ti, V, Cr, Mn, Cu,Zn, Au and Ag.
 21. The method of claim 12 wherein said catalyst metal isat least one selected from the group consisting of Fe, Co, Ni, Ru, Rh,Pd, Os, Ir, Pt, Sc, Ti, V, Cr, Mn, Cu, Zn, Au and Ag.
 22. A method ofmanufacturing a semiconductor device comprising the steps of:forming asemiconductor film comprising silicon on an insulating surface;disposing a catalyst containing material in contact with saidsemiconductor film, said catalyst capable of promoting a crystallizationof silicon; crystallizing said semiconductor film with the aid of saidcatalyst; oxidizing a surface of said semiconductor film to form anoxide layer thereon; and removing said oxide film in order to expose asurface of said semiconductor film.
 23. The method of claim 22 whereinsaid oxide layer is formed by thermal oxidation.
 24. The method of claim22 wherein said oxide layer is formed by photo oxidation.
 25. The methodof claim 22 wherein said catalyst metal is at least one selected fromthe group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Sc, Ti, V,Cr, Mn, Cu, Zn, Au and Ag.
 26. A method of manufacturing a semiconductordevice comprising the steps of:forming a semiconductor film comprisingsilicon on an insulating surface; disposing a catalyst containingmaterial in contact with said semiconductor film, said catalyst capableof promoting a crystallization of silicon; crystallizing saidsemiconductor film with the aid of said catalyst by heating; furthercrystallizing said semiconductor film by irradiating said semiconductorfilm with laser light after said heating; oxidizing a surface of saidsemiconductor film to form an oxide layer thereon; and removing saidoxide film in order to expose a surface of said semiconductor film. 27.The method of claim 26 wherein said oxide layer is formed by thermaloxidation.
 28. The method of claim 26 wherein said oxide layer is formedby photo oxidation.
 29. The method of claim 26 wherein said catalystmetal is at least one selected from the group consisting of Fe, Co, Ni,Ru, Rh, Pd, Os, Ir, Pt, Sc, Ti, V, Cr, Mn, Cu, Zn, Au and Ag.